1. Field of the Invention
The invention relates to a lock set, more particularly to a reinforced cylindrical door lock set.
2. Description of the Related Art
Referring to FIG. 1, a conventional cylindrical door lock set is shown to comprise an outer door knob (A) , an inner door knob (B), a turning mechanism (C), a knob support unit (D) and a latch unit (E). The knob support unit (D) includes inner and outer knob supporting plates (F, G) and a pair of bolts (H). The outer knob supporting plate (G) is formed with a central hole to permit the extension of the turning mechanism (C) therethrough. The outer knob supporting plate (G) has an outer side which is connected to the outer door knob (A). The outer knob supporting plate (G) further has an inner side which is provided with a pair of posts (I) on two sides of the central hole. The posts (I) are hollow and are threaded internally. The inner knob supporting plate (F) is formed with a central hole to permit mounting of the inner door knob (B) on an outer side of the knob supporting plate (F) . The inner door knob (B) is formed with an axial hole (not shown) for receiving one end of a turn shaft (K) of the turning mechanism (C). The inner knob supporting plate (F) is further formed with a pair of holes (J) which are aligned with the posts (I). The bolts (H) pass through the holes (J) and engage the posts (I) to retain the inner and outer knob supporting plates (F, G) on two sides of a door.
Note that in order to mount the cylindrical door lock set on the door, the door should be formed with a transverse larger opening (N). A smaller opening is then bored through the door so that the axis of the smaller opening is transverse to that of the larger opening (N). When installing the latch unit (E), the latch unit (E) is inserted into the larger opening (N) via the smaller opening and is secured in place by a pair of screws which pass through a face plate. The latch unit (E) is formed with a shaft engaging hole (M) and side holes (L) on two sides of the shaft engaging hole (M). The side holes (L) permit the extension of the posts (I) of the outer knob supporting plate (G) therethrough so as to align with the holes (J) of the inner knob supporting plate (F), while the shaft engaging hole (M) permits the extension of the turn shaft (K) of the turning mechanism (C) therethrough so as to engage the inner door knob (B). The bolts (H) then pass through the holes (J) and engage the posts (I) to retain the inner and outer knob supporting plates (F, G) on two sides of the door. When one of the outer and inner door knobs (A, B) is turned, the turn shaft (K) of the turning mechanism (C) turns therewith, thereby activating the latch unit (E) so as to permit opening of the door.
Since the cylindrical door lock set is provided on the larger opening (N) of the door, a relatively large space is formed between the inner and outer knob supporting plates (F, G). The cross-sectional size of the posts (I) cannot be increased and is limited by the size of the side holes (L) of the latch unit (E). Therefore, even though the inner and outer knob supporting plates (F, G) are secured tightly on the door by means of the bolts (H), the protection offered by the conventional cylindrical door lock set can be easily overcome by a thief by striking the cylindrical door lock set with a heavy object or by using a wrench to force the rotation of the outer knob supporting plate (G).